Harmonization of raster scan and rectangular tile groups in video coding

ABSTRACT

A video coding mechanism is disclosed. The mechanism includes partitioning a picture into a plurality of tiles. A number of the tiles are included in a tile group. A flag is also encoded into a parameter set of a bitstream. The flag is set to a first value when the tile group is a raster scan tile group and a second value when the tile group is a rectangular tile group. The tiles are encoded into the bitstream based on the tile group. The bitstream is stored for communication toward a decoder.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of International ApplicationNo. PCT/US2019/066884, filed Dec. 17, 2019 by FNU Hendry, et. al., andtitled “Harmonization of Raster Scan And Rectangular Tile Groups InVideo Coding,” which claims the benefit of U.S. Provisional PatentApplication No. 62/780,771, filed Dec. 17, 2018 by FNU Hendry, et. al.,and titled “Harmonization of Raster-scan and Rectangular Tile Group,”and U.S. Provisional Patent Application No. 62/848,149, filed May 15,2019 by FNU Hendry, et. al., and titled “Harmonization of Raster-scanand Rectangular Tile Group,” which are hereby incorporated by reference.

TECHNICAL FIELD

The present disclosure is generally related to video coding, and isspecifically related to mechanisms for partitioning images into tilegroups to support increased compression in video coding.

BACKGROUND

The amount of video data needed to depict even a relatively short videocan be substantial, which may result in difficulties when the data is tobe streamed or otherwise communicated across a communications networkwith limited bandwidth capacity. Thus, video data is generallycompressed before being communicated across modern daytelecommunications networks. The size of a video could also be an issuewhen the video is stored on a storage device because memory resourcesmay be limited. Video compression devices often use software and/orhardware at the source to code the video data prior to transmission orstorage, thereby decreasing the quantity of data needed to representdigital video images. The compressed data is then received at thedestination by a video decompression device that decodes the video data.With limited network resources and ever increasing demands of highervideo quality, improved compression and decompression techniques thatimprove compression ratio with little to no sacrifice in image qualityare desirable.

SUMMARY

In an embodiment, the disclosure includes a method implemented in anencoder, the method comprising: partitioning, by a processor of theencoder, a picture into a plurality of tiles; assigning, by theprocessor, a number of the tiles into a tile group; encoding, by theprocessor, a flag set to a first value when the tile group is a rasterscan tile group and a second value when the tile group is a rectangulartile group, wherein the flag is encoded into a parameter set of abitstream; encoding, by the processor, the tiles into the bitstreambased on the tile group; and storing, in a memory of the encoder, thebitstream for communication toward a decoder. Some video coding systemsemploy tile groups containing tiles assigned in raster scan order. Othersystems employ rectangular tile groups instead in order to supportsub-picture extraction in virtual reality (VR), teleconferencing, andother region of interest based coding schemes. Still other systems allowan encoder to select which type of tile group to use depending on thetype of video coding application. The present aspects includes a flagwhich indicates whether the corresponding tile group is raster scan orrectangular. This approach alerts the decoder to the proper tile groupcoding scheme to support proper decoding. Hence, the disclosed flagallows a encoder/decoder (codec) to support multiple tile group schemesfor different use cases, and hence increases the functionality of boththe encoder and decoder. Further, signaling the disclosed flag mayincrease coding efficiency, and hence reduce memory resource usage,processing resource usage, and/or network resource usage at the encoderand/or the decoder.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the flag is a rectangular tile group flag.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the parameter set into which the flag isencoded is a sequence parameter set.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the parameter set into which the flag isencoded is a picture parameter set.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, further comprising encoding in the bitstream, bythe processor, an identifier of a first tile of the tile group and anidentifier of a last tile of the tile group to indicate the tilesincluded in the tile group.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the identifier of the first tile of thetile group and the identifier of the last tile of the tile group areencoded in a tile group header in the bitstream.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein when the tile group is the raster scan tilegroup, tile inclusion in the tile group is determined by: determining anumber of tiles between the first tile of the tile group and the lasttile of the tile group as a number of tiles in the tile group; anddetermining tile inclusion based on the number of tiles in the tilegroup.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein when the tile group is the rectangular tilegroup, the tile inclusion in the tile group is determined by:determining a delta value between the first tile of the tile group andthe last tile of the tile group; determining a number of tile group rowsbased on the delta value and a number of tile columns in the picture;determining a number of tile group columns based on the delta value andthe number of tile columns in the picture; and determining the tileinclusion based on the number of tile group rows and the number of tilegroup columns.

In an embodiment, the disclosure includes a method implemented in adecoder, the method comprising: receiving, by a processor of the decodervia a receiver, a bitstream including a picture partitioned into aplurality of tiles, wherein a number of the tiles are included in a tilegroup; obtaining, by the processor, a flag from a parameter set of thebitstream; determining, by the processor, the tile group is a rasterscan tile group when the flag is set to a first value; determining, bythe processor, the tile group is a rectangular tile group when the flagis set to a second value; determining, by the processor, tile inclusionfor the tile group based on whether the tile group is the raster scantile group or rectangular tile group; decoding, by the processor, thetiles to generate decoded tiles based on the tile group; and generating,by the processor, a reconstructed video sequence for display based onthe decoded tiles. Some video coding systems employ tile groupscontaining tiles assigned in raster scan order. Other systems employrectangular tile groups instead in order to support sub-pictureextraction in VR, teleconferencing, and other region of interest basedcoding schemes. Still other systems allow an encoder to select whichtype of tile group to use depending on the type of video codingapplication. The present aspects includes a flag which indicates whetherthe corresponding tile group is raster scan or rectangular. Thisapproach alerts the decoder to the proper tile group coding scheme tosupport proper decoding. Hence, the disclosed flag allows a codec tosupport multiple tile group schemes for different use cases, and henceincreases the functionality of both the encoder and decoder. Further,signaling the disclosed flag may increase coding efficiency, and hencereduce memory resource usage, processing resource usage, and/or networkresource usage at the encoder and/or the decoder.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the flag is a rectangular tile group flag.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the parameter set including the flag is asequence parameter set.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the parameter set including the flag is apicture parameter set.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, further obtaining, by the processor, an identifierof a first tile of the tile group and an identifier of a last tile ofthe tile group to determine the tiles included in the tile group.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the identifier of the first tile of thetile group and the identifier of the last tile of the tile group areobtained from a tile group header in the bitstream.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein when the tile group is the raster scan tilegroup, tile inclusion in the tile group is determined by: determining anumber of tiles between the first tile of the tile group and the lasttile of the tile group as a number of tiles in the tile group; anddetermining tile inclusion based on the number of tiles in the tilegroup.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein when the tile group is the rectangular tilegroup, the tile inclusion in the tile group is determined by:determining a delta value between the first tile of the tile group andthe last tile of the tile group; determining a number of tile group rowsbased on the delta value and a number of tile columns in the picture;determining a number of tile group columns based on the delta value andthe number of tile columns in the picture; and determining the tileinclusion based on the number of tile group rows and the number of tilegroup columns.

In an embodiment, the disclosure includes a video coding devicecomprising: a processor, a receiver coupled to the processor, and atransmitter coupled to the processor, the processor, receiver, andtransmitter configured to perform the method of any of any of thepreceding aspects.

In an embodiment, the disclosure includes a non-transitory computerreadable medium comprising a computer program product for use by a videocoding device, the computer program product comprising computerexecutable instructions stored on the non-transitory computer readablemedium such that when executed by a processor cause the video codingdevice to perform the method of any of any of the preceding aspects.

In an embodiment, the disclosure includes an encoder comprising: apartitioning means for partitioning a picture into a plurality of tiles;an including means for including a number of the tiles into a tilegroup; an encoding means for: encoding a flag set to a first value whenthe tile group is a raster scan tile group and a second value when thetile group is a rectangular tile group, wherein the flag is encoded intoa parameter set of a bitstream; and encoding the tiles into thebitstream based on tile inclusion; and a storing means for storing thebitstream for communication toward a decoder.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the encoder is further configured toperform the method of any of any of the preceding aspects.

In an embodiment, the disclosure includes a decoder comprising: areceiving means for receiving a bitstream including a picturepartitioned into a plurality of tiles, wherein a number of the tiles areincluded in a tile group; an obtaining means for obtaining a flag from aparameter set of the bitstream; a determining means for: determining thetile group is a raster scan tile group when the flag is set to a firstvalue; determining the tile group is a rectangular tile group when theflag is set to a second value; and determining tile inclusion for thetile group based on whether the tile group is the raster scan tile groupor rectangular tile group; a decoding means for decoding the tiles togenerate decoded tiles based on the tile group; and a generating meansfor generating a reconstructed video sequence for display based on thedecoded tiles.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the decoder is further configured toperform the method of any of the preceding aspects.

For the purpose of clarity, any one of the foregoing embodiments may becombined with any one or more of the other foregoing embodiments tocreate a new embodiment within the scope of the present disclosure.

These and other features will be more clearly understood from thefollowing detailed description taken in conjunction with theaccompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this disclosure, reference is nowmade to the following brief description, taken in connection with theaccompanying drawings and detailed description, wherein like referencenumerals represent like parts.

FIG. 1 is a flowchart of an example method of coding a video signal.

FIG. 2 is a schematic diagram of an example coding and decoding (codec)system for video coding.

FIG. 3 is a schematic diagram illustrating an example video encoder.

FIG. 4 is a schematic diagram illustrating an example video decoder.

FIG. 5 is a schematic diagram illustrating an example bitstreamcontaining an encoded video sequence.

FIG. 6 is a schematic diagram illustrating an example picturepartitioned into raster scan tile groups.

FIG. 7 is a schematic diagram illustrating an example picturepartitioned into rectangular tile groups.

FIG. 8 is a schematic diagram of an example video coding device.

FIG. 9 is a flowchart of an example method of encoding a picture into abitstream.

FIG. 10 is a flowchart of an example method of decoding a picture from abitstream.

FIG. 11 is a schematic diagram of an example system for coding a videosequence of pictures in a bitstream.

DETAILED DESCRIPTION

It should be understood at the outset that although an illustrativeimplementation of one or more embodiments are provided below, thedisclosed systems and/or methods may be implemented using any number oftechniques, whether currently known or in existence. The disclosureshould in no way be limited to the illustrative implementations,drawings, and techniques illustrated below, including the exemplarydesigns and implementations illustrated and described herein, but may bemodified within the scope of the appended claims along with their fullscope of equivalents.

Various acronyms are employed herein, such as coding tree block (CTB),coding tree unit (CTU), coding unit (CU), coded video sequence (CVS),Joint Video Experts Team (JVET), motion constrained tile set (MCTS),maximum transfer unit (MTU), network abstraction layer (NAL), pictureorder count (POC), raw byte sequence payload (RBSP), sequence parameterset (SPS), versatile video coding (VVC), and working draft (WD).

Many video compression techniques can be employed to reduce the size ofvideo files with minimal loss of data. For example, video compressiontechniques can include performing spatial (e.g., intra-picture)prediction and/or temporal (e.g., inter-picture) prediction to reduce orremove data redundancy in video sequences. For block-based video coding,a video slice (e.g., a video picture or a portion of a video picture)may be partitioned into video blocks, which may also be referred to astreeblocks, coding tree blocks (CTBs), coding tree units (CTUs), codingunits (CUs), and/or coding nodes. Video blocks in an intra-coded (I)slice of a picture are coded using spatial prediction with respect toreference samples in neighboring blocks in the same picture. Videoblocks in an inter-coded unidirectional prediction (P) or bidirectionalprediction (B) slice of a picture may be coded by employing spatialprediction with respect to reference samples in neighboring blocks inthe same picture or temporal prediction with respect to referencesamples in other reference pictures. Pictures may be referred to asframes and/or images, and reference pictures may be referred to asreference frames and/or reference images. Spatial or temporal predictionresults in a predictive block representing an image block. Residual datarepresents pixel differences between the original image block and thepredictive block. Accordingly, an inter-coded block is encoded accordingto a motion vector that points to a block of reference samples formingthe predictive block and the residual data indicating the differencebetween the coded block and the predictive block. An intra-coded blockis encoded according to an intra-coding mode and the residual data. Forfurther compression, the residual data may be transformed from the pixeldomain to a transform domain. These result in residual transformcoefficients, which may be quantized. The quantized transformcoefficients may initially be arranged in a two-dimensional array. Thequantized transform coefficients may be scanned in order to produce aone-dimensional vector of transform coefficients. Entropy coding may beapplied to achieve even more compression. Such video compressiontechniques are discussed in greater detail below.

To ensure an encoded video can be accurately decoded, video is encodedand decoded according to corresponding video coding standards. Videocoding standards include International Telecommunication Union (ITU)Standardization Sector (ITU-T) H.261, International Organization forStandardization/International Electrotechnical Commission (ISO/IEC)Motion Picture Experts Group (MPEG)-1 Part 2, ITU-T H.262 or ISO/IECMPEG-2 Part 2, ITU-T H.263, ISO/IEC MPEG-4 Part 2, Advanced Video Coding(AVC), also known as ITU-T H.264 or ISO/IEC MPEG-4 Part 10, and HighEfficiency Video Coding (HEVC), also known as ITU-T H.265 or MPEG-H Part2. AVC includes extensions such as Scalable Video Coding (SVC),Multiview Video Coding (MVC) and Multiview Video Coding plus Depth(MVC+D), and three dimensional (3D) AVC (3D-AVC). HEVC includesextensions such as Scalable HEVC (SHVC), Multiview HEVC (MV-HEVC), and3D HEVC (3D-HEVC). The joint video experts team (JVET) of ITU-T andISO/IEC has begun developing a video coding standard referred to asVersatile Video Coding (VVC). VVC is included in a Working Draft (WD),which includes JVET-L1001-v5.

In order to code a video image, the image is first partitioned, and thepartitions are coded into a bitstream. Various picture partitioningschemes are available. For example, an image can be partitioned intoregular slices, dependent slices, tiles, and/or according to WavefrontParallel Processing (WPP). For simplicity, HEVC restricts encoders sothat only regular slices, dependent slices, tiles, WPP, and combinationsthereof can be used when partitioning a slice into groups of CTBs forvideo coding. Such partitioning can be applied to support MaximumTransfer Unit (MTU) size matching, parallel processing, and reducedend-to-end delay. MTU denotes the maximum amount of data that can betransmitted in a single packet. If a packet payload is in excess of theMTU, that payload is split into two packets through a process calledfragmentation.

A regular slice, also referred to simply as a slice, is a partitionedportion of an image that can be reconstructed independently from otherregular slices within the same picture, notwithstanding someinterdependencies due to loop filtering operations. Each regular sliceis encapsulated in its own Network Abstraction Layer (NAL) unit fortransmission. Further, in-picture prediction (intra sample prediction,motion information prediction, coding mode prediction) and entropycoding dependency across slice boundaries may be disabled to supportindependent reconstruction. Such independent reconstruction supportsparallelization. For example, regular slice based parallelizationemploys minimal inter-processor or inter-core communication. However, aseach regular slice is independent, each slice is associated with aseparate slice header. The use of regular slices can incur a substantialcoding overhead due to the bit cost of the slice header for each sliceand due to the lack of prediction across the slice boundaries. Further,regular slices may be employed to support matching for MTU sizerequirements. Specifically, as a regular slice is encapsulated in aseparate NAL unit and can be independently coded, each regular sliceshould be smaller than the MTU in MTU schemes to avoid breaking theslice into multiple packets. As such, the goal of parallelization andthe goal of MTU size matching may place contradicting demands to a slicelayout in a picture.

Dependent slices are similar to regular slices, but have shortened sliceheaders and allow partitioning of the image treeblock boundaries withoutbreaking in-picture prediction. Accordingly, dependent slices allow aregular slice to be fragmented into multiple NAL units, which providesreduced end-to-end delay by allowing a part of a regular slice to besent out before the encoding of the entire regular slice is complete.

A tile is a partitioned portion of an image created by horizontal andvertical boundaries that create columns and rows of tiles. Tiles may becoded in raster scan order (right to left and top to bottom). The scanorder of CTBs is local within a tile. Accordingly, CTBs in a first tileare coded in raster scan order, before proceeding to the CTBs in thenext tile. Similar to regular slices, tiles break in-picture predictiondependencies as well as entropy decoding dependencies. However, tilesmay not be included into individual NAL units, and hence tiles may notbe used for MTU size matching. Each tile can be processed by oneprocessor/core, and the inter-processor/inter-core communicationemployed for in-picture prediction between processing units decodingneighboring tiles may be limited to conveying a shared slice header(when adjacent tiles are in the same slice), and performing loopfiltering related sharing of reconstructed samples and metadata. Whenmore than one tile is included in a slice, the entry point byte offsetfor each tile other than the first entry point offset in the slice maybe signaled in the slice header. For each slice and tile, at least oneof the following conditions should be fulfilled: 1) all coded treeblocksin a slice belong to the same tile; and 2) all coded treeblocks in atile belong to the same slice.

In WPP, the image is partitioned into single rows of CTBs. Entropydecoding and prediction mechanisms may use data from CTBs in other rows.Parallel processing is made possible through parallel decoding of CTBrows. For example, a current row may be decoded in parallel with apreceding row. However, decoding of the current row is delayed from thedecoding process of the preceding rows by two CTBs. This delay ensuresthat data related to the CTB above and the CTB above and to the right ofthe current CTB in the current row is available before the current CTBis coded. This approach appears as a wavefront when representedgraphically. This staggered start allows for parallelization with up toas many processors/cores as the image contains CTB rows. Becausein-picture prediction between neighboring treeblock rows within apicture is permitted, the inter-processor/inter-core communication toenable in-picture prediction can be substantial. The WPP partitioningdoes consider NAL unit sizes. Hence, WPP does not support MTU sizematching. However, regular slices can be used in conjunction with WPP,with certain coding overhead, to implement MTU size matching as desired.

Tiles may also include motion constrained tile sets. A motionconstrained tile set (MCTS) is a tile set designed such that associatedmotion vectors are restricted to point to full-sample locations insidethe MCTS and to fractional-sample locations that require onlyfull-sample locations inside the MCTS for interpolation. Further, theusage of motion vector candidates for temporal motion vector predictionderived from blocks outside the MCTS is disallowed. This way, each MCTSmay be independently decoded without the existence of tiles not includedin the MCTS. Temporal MCTSs supplemental enhancement information (SEI)messages may be used to indicate the existence of MCTSs in the bitstreamand signal the MCTSs. The MCTSs SEI message provides supplementalinformation that can be used in the MCTS sub-bitstream extraction(specified as part of the semantics of the SEI message) to generate aconforming bitstream for a MCTS. The information includes a number ofextraction information sets, each defining a number of MCTSs andcontaining raw bytes sequence payload (RBSP) bytes of the replacementvideo parameter sets (VPSs), sequence parameter sets (SPSs), and pictureparameter sets (PPSs) to be used during the MCTS sub-bitstreamextraction process. When extracting a sub-bitstream according to theMCTS sub-bitstream extraction process, parameter sets (VPSs, SPSs, andPPSs) may be rewritten or replaced, and slice headers may updatedbecause one or all of the slice address related syntax elements(including first_slice_segment_in_pic_flag and slice_segment_address)may employ different values in the extracted sub-bitstream.

The present disclosure is related to various tiling schemes.Specifically, when an image is partitioned into tiles, such tiles can beassigned to tile groups. A tile group is a set of related tiles that canbe separately extracted and coded, for example to support display of aregion of interest and/or to support parallel processing. Tiles can beassigned to tile groups to allow group wide application of correspondingparameters, functions, coding tools, etc. For example, a tile group maycontain a MCTS. As another example, tile groups may be processed and/orextracted separately. Some systems employ a raster scan mechanism tocreate corresponding tile groups. As used herein, a raster scan tilegroup is a tile group that is created by assigning tiles in a rasterscan order. Raster scan order proceeds continuously from right to leftand top to bottom between a first tile and a last tile. Raster scan tilegroups may be useful for some applications, for example to supportparallel processing.

However, raster scan tile groups may not be efficient in some cases. Forexample, in virtual reality (VR) applications, an environment isrecorded as a sphere encoded into a picture. A user can then experiencethe environment by viewing a user selected sub-picture of the picture. Auser selected sub-picture may be referred to as a region of interest.Allowing the user to selectively perceive a portion of the environmentcreates the sensation that the user is present in that environment. Assuch, non-selected portions of the picture may not be viewed and hencediscarded. Accordingly, the user selected sub-picture may be treateddifferently from the non-selected sub-picture (e.g., the non-selectedsub-picture may be signaled at lower resolution, may be processed usingsimpler mechanisms during rendering, etc.) Tile groups allow suchdifferential treatment between sub-pictures. However, the user selectedsub-picture is generally a rectangle and/or a square area. Accordingly,raster scan tile groups may not be useful for such use cases.

To overcome these issues, some systems employ rectangular tile groups. Arectangular tile group is a tile group containing a set of tiles that,when taken together, result in a rectangular shape. A rectangular shape,as used herein, is a shape with exactly four sides connected such thateach side is connected to two other sides, each at a ninety degreeangle. Both tile group approaches (e.g., raster scan tile group andrectangular tile group) may have advantages and disadvantages.Accordingly, video coding systems may wish to support both approaches.However, video coding systems may be unable to efficiently signal tilegroup usage when both approaches are available. For example, a simplemerging of the signaling of these approaches may result in complicatedsyntax structure that is inefficient and/or processor intensive at theencoder and/or the decoder. The present disclosure presents mechanismsto address these and other issues in the video coding arts.

Disclosed herein are various mechanisms to harmonize the usage of rasterscan tile groups and rectangular tile groups by employing simple andcompact signaling. Such signaling increases coding efficiency, and hencereduces memory resource usage, processing resource usage, and/or networkresource usage at the encoder and/or the decoder. In order to harmonizethese approaches, the encoder can signal a flag indicating which type oftile group is employed. For example, the flag may be a rectangular tilegroup flag, which may be signaled in a parameter set, such as a SPSand/or a PPS. The flag can indicate whether the encoder is using rasterscan tile groups or rectangular tile groups. The encoder can thenindicate tile group membership by simply signaling the first and lasttile in the tile group. Based on the first tile, the last tile, and theindication of the tile group type, the decoder can determine which tilesare included in a tile group. Accordingly, a full list of all tiles ineach tile group may be omitted from the bitstream, which increasescoding efficiency. For example, if the tile group is a raster scan tilegroup, the tiles assigned to the tile group can be determined bydetermining a number of tiles between the first tile and the last tileof the tile group, and adding that many tiles, with identifiers betweenthe first tile and last tile, to the tile group. If the tile group is arectangular tile group, a different approach can be used. For example, adelta value can be determined between the first tile and the last tileof the tile group. A number of tile group rows and a number of tilegroup columns can then be determined based on the delta value and thenumber of tile columns in the picture. The tiles in the tile group canthen be determined based on the number of tile group rows and the numberof tile group columns. These and other examples are described in detailbelow.

FIG. 1 is a flowchart of an example operating method 100 of coding avideo signal. Specifically, a video signal is encoded at an encoder. Theencoding process compresses the video signal by employing variousmechanisms to reduce the video file size. A smaller file size allows thecompressed video file to be transmitted toward a user, while reducingassociated bandwidth overhead. The decoder then decodes the compressedvideo file to reconstruct the original video signal for display to anend user. The decoding process generally mirrors the encoding process toallow the decoder to consistently reconstruct the video signal.

At step 101, the video signal is input into the encoder. For example,the video signal may be an uncompressed video file stored in memory. Asanother example, the video file may be captured by a video capturedevice, such as a video camera, and encoded to support live streaming ofthe video. The video file may include both an audio component and avideo component. The video component contains a series of image framesthat, when viewed in a sequence, gives the visual impression of motion.The frames contain pixels that are expressed in terms of light, referredto herein as luma components (or luma samples), and color, which isreferred to as chroma components (or color samples). In some examples,the frames may also contain depth values to support three dimensionalviewing.

At step 103, the video is partitioned into blocks. Partitioning includessubdividing the pixels in each frame into square and/or rectangularblocks for compression. For example, in High Efficiency Video Coding(HEVC) (also known as H.265 and MPEG-H Part 2) the frame can first bedivided into coding tree units (CTUs), which are blocks of a predefinedsize (e.g., sixty-four pixels by sixty-four pixels). The CTUs containboth luma and chroma samples. Coding trees may be employed to divide theCTUs into blocks and then recursively subdivide the blocks untilconfigurations are achieved that support further encoding. For example,luma components of a frame may be subdivided until the individual blockscontain relatively homogenous lighting values. Further, chromacomponents of a frame may be subdivided until the individual blockscontain relatively homogenous color values. Accordingly, partitioningmechanisms vary depending on the content of the video frames.

At step 105, various compression mechanisms are employed to compress theimage blocks partitioned at step 103. For example, inter-predictionand/or intra-prediction may be employed. Inter-prediction is designed totake advantage of the fact that objects in a common scene tend to appearin successive frames. Accordingly, a block depicting an object in areference frame need not be repeatedly described in adjacent frames.Specifically, an object, such as a table, may remain in a constantposition over multiple frames. Hence the table is described once andadjacent frames can refer back to the reference frame. Pattern matchingmechanisms may be employed to match objects over multiple frames.Further, moving objects may be represented across multiple frames, forexample due to object movement or camera movement. As a particularexample, a video may show an automobile that moves across the screenover multiple frames. Motion vectors can be employed to describe suchmovement. A motion vector is a two-dimensional vector that provides anoffset from the coordinates of an object in a frame to the coordinatesof the object in a reference frame. As such, inter-prediction can encodean image block in a current frame as a set of motion vectors indicatingan offset from a corresponding block in a reference frame.

Intra-prediction encodes blocks in a common frame. Intra-predictiontakes advantage of the fact that luma and chroma components tend tocluster in a frame. For example, a patch of green in a portion of a treetends to be positioned adjacent to similar patches of green.Intra-prediction employs multiple directional prediction modes (e.g.,thirty-three in HEVC), a planar mode, and a direct current (DC) mode.The directional modes indicate that a current block is similar/the sameas samples of a neighbor block in a corresponding direction. Planar modeindicates that a series of blocks along a row/column (e.g., a plane) canbe interpolated based on neighbor blocks at the edges of the row. Planarmode, in effect, indicates a smooth transition of light/color across arow/column by employing a relatively constant slope in changing values.DC mode is employed for boundary smoothing and indicates that a block issimilar/the same as an average value associated with samples of all theneighbor blocks associated with the angular directions of thedirectional prediction modes. Accordingly, intra-prediction blocks canrepresent image blocks as various relational prediction mode valuesinstead of the actual values. Further, inter-prediction blocks canrepresent image blocks as motion vector values instead of the actualvalues. In either case, the prediction blocks may not exactly representthe image blocks in some cases. Any differences are stored in residualblocks. Transforms may be applied to the residual blocks to furthercompress the file.

At step 107, various filtering techniques may be applied. In HEVC, thefilters are applied according to an in-loop filtering scheme. The blockbased prediction discussed above may result in the creation of blockyimages at the decoder. Further, the block based prediction scheme mayencode a block and then reconstruct the encoded block for later use as areference block. The in-loop filtering scheme iteratively applies noisesuppression filters, de-blocking filters, adaptive loop filters, andsample adaptive offset (SAO) filters to the blocks/frames. These filtersmitigate such blocking artifacts so that the encoded file can beaccurately reconstructed. Further, these filters mitigate artifacts inthe reconstructed reference blocks so that artifacts are less likely tocreate additional artifacts in subsequent blocks that are encoded basedon the reconstructed reference blocks.

Once the video signal has been partitioned, compressed, and filtered,the resulting data is encoded in a bitstream at step 109. The bitstreamincludes the data discussed above as well as any signaling data desiredto support proper video signal reconstruction at the decoder. Forexample, such data may include partition data, prediction data, residualblocks, and various flags providing coding instructions to the decoder.The bitstream may be stored in memory for transmission toward a decoderupon request. The bitstream may also be broadcast and/or multicasttoward a plurality of decoders. The creation of the bitstream is aniterative process. Accordingly, steps 101, 103, 105, 107, and 109 mayoccur continuously and/or simultaneously over many frames and blocks.The order shown in FIG. 1 is presented for clarity and ease ofdiscussion, and is not intended to limit the video coding process to aparticular order.

The decoder receives the bitstream and begins the decoding process atstep 111. Specifically, the decoder employs an entropy decoding schemeto convert the bitstream into corresponding syntax and video data. Thedecoder employs the syntax data from the bitstream to determine thepartitions for the frames at step 111. The partitioning should match theresults of block partitioning at step 103. Entropy encoding/decoding asemployed in step 111 is now described. The encoder makes many choicesduring the compression process, such as selecting block partitioningschemes from several possible choices based on the spatial positioningof values in the input image(s). Signaling the exact choices may employa large number of bins. As used herein, a bin is a binary value that istreated as a variable (e.g., a bit value that may vary depending oncontext). Entropy coding allows the encoder to discard any options thatare clearly not viable for a particular case, leaving a set of allowableoptions. Each allowable option is then assigned a code word. The lengthof the code words is based on the number of allowable options (e.g., onebin for two options, two bins for three to four options, etc.) Theencoder then encodes the code word for the selected option. This schemereduces the size of the code words as the code words are as big asdesired to uniquely indicate a selection from a small sub-set ofallowable options as opposed to uniquely indicating the selection from apotentially large set of all possible options. The decoder then decodesthe selection by determining the set of allowable options in a similarmanner to the encoder. By determining the set of allowable options, thedecoder can read the code word and determine the selection made by theencoder.

At step 113, the decoder performs block decoding. Specifically, thedecoder employs reverse transforms to generate residual blocks. Then thedecoder employs the residual blocks and corresponding prediction blocksto reconstruct the image blocks according to the partitioning. Theprediction blocks may include both intra-prediction blocks andinter-prediction blocks as generated at the encoder at step 105. Thereconstructed image blocks are then positioned into frames of areconstructed video signal according to the partitioning data determinedat step 111. Syntax for step 113 may also be signaled in the bitstreamvia entropy coding as discussed above.

At step 115, filtering is performed on the frames of the reconstructedvideo signal in a manner similar to step 107 at the encoder. Forexample, noise suppression filters, de-blocking filters, adaptive loopfilters, and SAO filters may be applied to the frames to remove blockingartifacts. Once the frames are filtered, the video signal can be outputto a display at step 117 for viewing by an end user.

FIG. 2 is a schematic diagram of an example coding and decoding (codec)system 200 for video coding. Specifically, codec system 200 providesfunctionality to support the implementation of operating method 100.Codec system 200 is generalized to depict components employed in both anencoder and a decoder. Codec system 200 receives and partitions a videosignal as discussed with respect to steps 101 and 103 in operatingmethod 100, which results in a partitioned video signal 201. Codecsystem 200 then compresses the partitioned video signal 201 into a codedbitstream when acting as an encoder as discussed with respect to steps105, 107, and 109 in method 100. When acting as a decoder codec system200 generates an output video signal from the bitstream as discussedwith respect to steps 111, 113, 115, and 117 in operating method 100.The codec system 200 includes a general coder control component 211, atransform scaling and quantization component 213, an intra-pictureestimation component 215, an intra-picture prediction component 217, amotion compensation component 219, a motion estimation component 221, ascaling and inverse transform component 229, a filter control analysiscomponent 227, an in-loop filters component 225, a decoded picturebuffer component 223, and a header formatting and context adaptivebinary arithmetic coding (CABAC) component 231. Such components arecoupled as shown. In FIG. 2 , black lines indicate movement of data tobe encoded/decoded while dashed lines indicate movement of control datathat controls the operation of other components. The components of codecsystem 200 may all be present in the encoder. The decoder may include asubset of the components of codec system 200. For example, the decodermay include the intra-picture prediction component 217, the motioncompensation component 219, the scaling and inverse transform component229, the in-loop filters component 225, and the decoded picture buffercomponent 223. These components are now described.

The partitioned video signal 201 is a captured video sequence that hasbeen partitioned into blocks of pixels by a coding tree. A coding treeemploys various split modes to subdivide a block of pixels into smallerblocks of pixels. These blocks can then be further subdivided intosmaller blocks. The blocks may be referred to as nodes on the codingtree. Larger parent nodes are split into smaller child nodes. The numberof times a node is subdivided is referred to as the depth of thenode/coding tree. The divided blocks can be included in coding units(CUs) in some cases. For example, a CU can be a sub-portion of a CTUthat contains a luma block, red difference chroma (Cr) block(s), and ablue difference chroma (Cb) block(s) along with corresponding syntaxinstructions for the CU. The split modes may include a binary tree (BT),triple tree (TT), and a quad tree (QT) employed to partition a node intotwo, three, or four child nodes, respectively, of varying shapesdepending on the split modes employed. The partitioned video signal 201is forwarded to the general coder control component 211, the transformscaling and quantization component 213, the intra-picture estimationcomponent 215, the filter control analysis component 227, and the motionestimation component 221 for compression.

The general coder control component 211 is configured to make decisionsrelated to coding of the images of the video sequence into the bitstreamaccording to application constraints. For example, the general codercontrol component 211 manages optimization of bitrate/bitstream sizeversus reconstruction quality. Such decisions may be made based onstorage space/bandwidth availability and image resolution requests. Thegeneral coder control component 211 also manages buffer utilization inlight of transmission speed to mitigate buffer underrun and overrunissues. To manage these issues, the general coder control component 211manages partitioning, prediction, and filtering by the other components.For example, the general coder control component 211 may dynamicallyincrease compression complexity to increase resolution and increasebandwidth usage or decrease compression complexity to decreaseresolution and bandwidth usage. Hence, the general coder controlcomponent 211 controls the other components of codec system 200 tobalance video signal reconstruction quality with bit rate concerns. Thegeneral coder control component 211 creates control data, which controlsthe operation of the other components. The control data is alsoforwarded to the header formatting and CABAC component 231 to be encodedin the bitstream to signal parameters for decoding at the decoder.

The partitioned video signal 201 is also sent to the motion estimationcomponent 221 and the motion compensation component 219 forinter-prediction. A frame or slice of the partitioned video signal 201may be divided into multiple video blocks. Motion estimation component221 and the motion compensation component 219 perform inter-predictivecoding of the received video block relative to one or more blocks in oneor more reference frames to provide temporal prediction. Codec system200 may perform multiple coding passes, e.g., to select an appropriatecoding mode for each block of video data.

Motion estimation component 221 and motion compensation component 219may be highly integrated, but are illustrated separately for conceptualpurposes. Motion estimation, performed by motion estimation component221, is the process of generating motion vectors, which estimate motionfor video blocks. A motion vector, for example, may indicate thedisplacement of a coded object relative to a predictive block. Apredictive block is a block that is found to closely match the block tobe coded, in terms of pixel difference. A predictive block may also bereferred to as a reference block. Such pixel difference may bedetermined by sum of absolute difference (SAD), sum of square difference(SSD), or other difference metrics. HEVC employs several coded objectsincluding a CTU, coding tree blocks (CTBs), and CUs. For example, a CTUcan be divided into CTBs, which can then be divided into CBs forinclusion in CUs. A CU can be encoded as a prediction unit (PU)containing prediction data and/or a transform unit (TU) containingtransformed residual data for the CU. The motion estimation component221 generates motion vectors, PUs, and TUs by using a rate-distortionanalysis as part of a rate distortion optimization process. For example,the motion estimation component 221 may determine multiple referenceblocks, multiple motion vectors, etc. for a current block/frame, and mayselect the reference blocks, motion vectors, etc. having the bestrate-distortion characteristics. The best rate-distortioncharacteristics balance both quality of video reconstruction (e.g.,amount of data loss by compression) with coding efficiency (e.g., sizeof the final encoding).

In some examples, codec system 200 may calculate values for sub-integerpixel positions of reference pictures stored in decoded picture buffercomponent 223. For example, video codec system 200 may interpolatevalues of one-quarter pixel positions, one-eighth pixel positions, orother fractional pixel positions of the reference picture. Therefore,motion estimation component 221 may perform a motion search relative tothe full pixel positions and fractional pixel positions and output amotion vector with fractional pixel precision. The motion estimationcomponent 221 calculates a motion vector for a PU of a video block in aninter-coded slice by comparing the position of the PU to the position ofa predictive block of a reference picture. Motion estimation component221 outputs the calculated motion vector as motion data to headerformatting and CABAC component 231 for encoding and motion to the motioncompensation component 219.

Motion compensation, performed by motion compensation component 219, mayinvolve fetching or generating the predictive block based on the motionvector determined by motion estimation component 221. Again, motionestimation component 221 and motion compensation component 219 may befunctionally integrated, in some examples. Upon receiving the motionvector for the PU of the current video block, motion compensationcomponent 219 may locate the predictive block to which the motion vectorpoints. A residual video block is then formed by subtracting pixelvalues of the predictive block from the pixel values of the currentvideo block being coded, forming pixel difference values. In general,motion estimation component 221 performs motion estimation relative toluma components, and motion compensation component 219 uses motionvectors calculated based on the luma components for both chromacomponents and luma components. The predictive block and residual blockare forwarded to transform scaling and quantization component 213.

The partitioned video signal 201 is also sent to intra-pictureestimation component 215 and intra-picture prediction component 217. Aswith motion estimation component 221 and motion compensation component219, intra-picture estimation component 215 and intra-picture predictioncomponent 217 may be highly integrated, but are illustrated separatelyfor conceptual purposes. The intra-picture estimation component 215 andintra-picture prediction component 217 intra-predict a current blockrelative to blocks in a current frame, as an alternative to theinter-prediction performed by motion estimation component 221 and motioncompensation component 219 between frames, as described above. Inparticular, the intra-picture estimation component 215 determines anintra-prediction mode to use to encode a current block. In someexamples, intra-picture estimation component 215 selects an appropriateintra-prediction mode to encode a current block from multiple testedintra-prediction modes. The selected intra-prediction modes are thenforwarded to the header formatting and CABAC component 231 for encoding.

For example, the intra-picture estimation component 215 calculatesrate-distortion values using a rate-distortion analysis for the varioustested intra-prediction modes, and selects the intra-prediction modehaving the best rate-distortion characteristics among the tested modes.Rate-distortion analysis generally determines an amount of distortion(or error) between an encoded block and an original unencoded block thatwas encoded to produce the encoded block, as well as a bitrate (e.g., anumber of bits) used to produce the encoded block. The intra-pictureestimation component 215 calculates ratios from the distortions andrates for the various encoded blocks to determine which intra-predictionmode exhibits the best rate-distortion value for the block. In addition,intra-picture estimation component 215 may be configured to code depthblocks of a depth map using a depth modeling mode (DMM) based onrate-distortion optimization (RDO).

The intra-picture prediction component 217 may generate a residual blockfrom the predictive block based on the selected intra-prediction modesdetermined by intra-picture estimation component 215 when implemented onan encoder or read the residual block from the bitstream whenimplemented on a decoder. The residual block includes the difference invalues between the predictive block and the original block, representedas a matrix. The residual block is then forwarded to the transformscaling and quantization component 213. The intra-picture estimationcomponent 215 and the intra-picture prediction component 217 may operateon both luma and chroma components.

The transform scaling and quantization component 213 is configured tofurther compress the residual block. The transform scaling andquantization component 213 applies a transform, such as a discretecosine transform (DCT), a discrete sine transform (DST), or aconceptually similar transform, to the residual block, producing a videoblock comprising residual transform coefficient values. Wavelettransforms, integer transforms, sub-band transforms or other types oftransforms could also be used. The transform may convert the residualinformation from a pixel value domain to a transform domain, such as afrequency domain. The transform scaling and quantization component 213is also configured to scale the transformed residual information, forexample based on frequency. Such scaling involves applying a scalefactor to the residual information so that different frequencyinformation is quantized at different granularities, which may affectfinal visual quality of the reconstructed video. The transform scalingand quantization component 213 is also configured to quantize thetransform coefficients to further reduce bit rate. The quantizationprocess may reduce the bit depth associated with some or all of thecoefficients. The degree of quantization may be modified by adjusting aquantization parameter. In some examples, the transform scaling andquantization component 213 may then perform a scan of the matrixincluding the quantized transform coefficients. The quantized transformcoefficients are forwarded to the header formatting and CABAC component231 to be encoded in the bitstream.

The scaling and inverse transform component 229 applies a reverseoperation of the transform scaling and quantization component 213 tosupport motion estimation. The scaling and inverse transform component229 applies inverse scaling, transformation, and/or quantization toreconstruct the residual block in the pixel domain, e.g., for later useas a reference block which may become a predictive block for anothercurrent block. The motion estimation component 221 and/or motioncompensation component 219 may calculate a reference block by adding theresidual block back to a corresponding predictive block for use inmotion estimation of a later block/frame. Filters are applied to thereconstructed reference blocks to mitigate artifacts created duringscaling, quantization, and transform. Such artifacts could otherwisecause inaccurate prediction (and create additional artifacts) whensubsequent blocks are predicted.

The filter control analysis component 227 and the in-loop filterscomponent 225 apply the filters to the residual blocks and/or toreconstructed image blocks. For example, the transformed residual blockfrom the scaling and inverse transform component 229 may be combinedwith a corresponding prediction block from intra-picture predictioncomponent 217 and/or motion compensation component 219 to reconstructthe original image block. The filters may then be applied to thereconstructed image block. In some examples, the filters may instead beapplied to the residual blocks. As with other components in FIG. 2 , thefilter control analysis component 227 and the in-loop filters component225 are highly integrated and may be implemented together, but aredepicted separately for conceptual purposes. Filters applied to thereconstructed reference blocks are applied to particular spatial regionsand include multiple parameters to adjust how such filters are applied.The filter control analysis component 227 analyzes the reconstructedreference blocks to determine where such filters should be applied andsets corresponding parameters. Such data is forwarded to the headerformatting and CABAC component 231 as filter control data for encoding.The in-loop filters component 225 applies such filters based on thefilter control data. The filters may include a deblocking filter, anoise suppression filter, a SAO filter, and an adaptive loop filter.Such filters may be applied in the spatial/pixel domain (e.g., on areconstructed pixel block) or in the frequency domain, depending on theexample.

When operating as an encoder, the filtered reconstructed image block,residual block, and/or prediction block are stored in the decodedpicture buffer component 223 for later use in motion estimation asdiscussed above. When operating as a decoder, the decoded picture buffercomponent 223 stores and forwards the reconstructed and filtered blockstoward a display as part of an output video signal. The decoded picturebuffer component 223 may be any memory device capable of storingprediction blocks, residual blocks, and/or reconstructed image blocks.

The header formatting and CABAC component 231 receives the data from thevarious components of codec system 200 and encodes such data into acoded bitstream for transmission toward a decoder. Specifically, theheader formatting and CABAC component 231 generates various headers toencode control data, such as general control data and filter controldata. Further, prediction data, including intra-prediction and motiondata, as well as residual data in the form of quantized transformcoefficient data are all encoded in the bitstream. The final bitstreamincludes all information desired by the decoder to reconstruct theoriginal partitioned video signal 201. Such information may also includeintra-prediction mode index tables (also referred to as codeword mappingtables), definitions of encoding contexts for various blocks,indications of most probable intra-prediction modes, an indication ofpartition information, etc. Such data may be encoded by employingentropy coding. For example, the information may be encoded by employingcontext adaptive variable length coding (CAVLC), CABAC, syntax-basedcontext-adaptive binary arithmetic coding (SBAC), probability intervalpartitioning entropy (PIPE) coding, or another entropy coding technique.Following the entropy coding, the coded bitstream may be transmitted toanother device (e.g., a video decoder) or archived for latertransmission or retrieval.

FIG. 3 is a block diagram illustrating an example video encoder 300.Video encoder 300 may be employed to implement the encoding functions ofcodec system 200 and/or implement steps 101, 103, 105, 107, and/or 109of operating method 100. Encoder 300 partitions an input video signal,resulting in a partitioned video signal 301, which is substantiallysimilar to the partitioned video signal 201. The partitioned videosignal 301 is then compressed and encoded into a bitstream by componentsof encoder 300.

Specifically, the partitioned video signal 301 is forwarded to anintra-picture prediction component 317 for intra-prediction. Theintra-picture prediction component 317 may be substantially similar tointra-picture estimation component 215 and intra-picture predictioncomponent 217. The partitioned video signal 301 is also forwarded to amotion compensation component 321 for inter-prediction based onreference blocks in a decoded picture buffer component 323. The motioncompensation component 321 may be substantially similar to motionestimation component 221 and motion compensation component 219. Theprediction blocks and residual blocks from the intra-picture predictioncomponent 317 and the motion compensation component 321 are forwarded toa transform and quantization component 313 for transform andquantization of the residual blocks. The transform and quantizationcomponent 313 may be substantially similar to the transform scaling andquantization component 213. The transformed and quantized residualblocks and the corresponding prediction blocks (along with associatedcontrol data) are forwarded to an entropy coding component 331 forcoding into a bitstream. The entropy coding component 331 may besubstantially similar to the header formatting and CABAC component 231.

The transformed and quantized residual blocks and/or the correspondingprediction blocks are also forwarded from the transform and quantizationcomponent 313 to an inverse transform and quantization component 329 forreconstruction into reference blocks for use by the motion compensationcomponent 321. The inverse transform and quantization component 329 maybe substantially similar to the scaling and inverse transform component229. In-loop filters in an in-loop filters component 325 are alsoapplied to the residual blocks and/or reconstructed reference blocks,depending on the example. The in-loop filters component 325 may besubstantially similar to the filter control analysis component 227 andthe in-loop filters component 225. The in-loop filters component 325 mayinclude multiple filters as discussed with respect to in-loop filterscomponent 225. The filtered blocks are then stored in a decoded picturebuffer component 323 for use as reference blocks by the motioncompensation component 321. The decoded picture buffer component 323 maybe substantially similar to the decoded picture buffer component 223.

FIG. 4 is a block diagram illustrating an example video decoder 400.Video decoder 400 may be employed to implement the decoding functions ofcodec system 200 and/or implement steps 111, 113, 115, and/or 117 ofoperating method 100. Decoder 400 receives a bitstream, for example froman encoder 300, and generates a reconstructed output video signal basedon the bitstream for display to an end user.

The bitstream is received by an entropy decoding component 433. Theentropy decoding component 433 is configured to implement an entropydecoding scheme, such as CAVLC, CABAC, SBAC, PIPE coding, or otherentropy coding techniques. For example, the entropy decoding component433 may employ header information to provide a context to interpretadditional data encoded as codewords in the bitstream. The decodedinformation includes any desired information to decode the video signal,such as general control data, filter control data, partitioninformation, motion data, prediction data, and quantized transformcoefficients from residual blocks. The quantized transform coefficientsare forwarded to an inverse transform and quantization component 429 forreconstruction into residual blocks. The inverse transform andquantization component 429 may be similar to inverse transform andquantization component 329.

The reconstructed residual blocks and/or prediction blocks are forwardedto intra-picture prediction component 417 for reconstruction into imageblocks based on intra-prediction operations. The intra-pictureprediction component 417 may be similar to intra-picture estimationcomponent 215 and an intra-picture prediction component 217.Specifically, the intra-picture prediction component 417 employsprediction modes to locate a reference block in the frame and applies aresidual block to the result to reconstruct intra-predicted imageblocks. The reconstructed intra-predicted image blocks and/or theresidual blocks and corresponding inter-prediction data are forwarded toa decoded picture buffer component 423 via an in-loop filters component425, which may be substantially similar to decoded picture buffercomponent 223 and in-loop filters component 225, respectively. Thein-loop filters component 425 filters the reconstructed image blocks,residual blocks and/or prediction blocks, and such information is storedin the decoded picture buffer component 423. Reconstructed image blocksfrom decoded picture buffer component 423 are forwarded to a motioncompensation component 421 for inter-prediction. The motion compensationcomponent 421 may be substantially similar to motion estimationcomponent 221 and/or motion compensation component 219. Specifically,the motion compensation component 421 employs motion vectors from areference block to generate a prediction block and applies a residualblock to the result to reconstruct an image block. The resultingreconstructed blocks may also be forwarded via the in-loop filterscomponent 425 to the decoded picture buffer component 423. The decodedpicture buffer component 423 continues to store additional reconstructedimage blocks, which can be reconstructed into frames via the partitioninformation. Such frames may also be placed in a sequence. The sequenceis output toward a display as a reconstructed output video signal.

FIG. 5 is a schematic diagram illustrating an example bitstream 500containing an encoded video sequence. For example, the bitstream 500 canbe generated by a codec system 200 and/or an encoder 300 for decoding bya codec system 200 and/or a decoder 400. As another example, thebitstream 500 may be generated by an encoder at step 109 of method 100for use by a decoder at step 111.

The bitstream 500 includes a sequence parameter set (SPS) 510, aplurality of picture parameter sets (PPSs) 512, tile group headers 514,and image data 520. An SPS 510 contains sequence data common to all thepictures in the video sequence contained in the bitstream 500. Such datacan include picture sizing, bit depth, coding tool parameters, bit raterestrictions, etc. The PPS 512 contains parameters that are specific toone or more corresponding pictures. Hence, each picture in a videosequence may refer to one PPS 512. The PPS 512 can indicate coding toolsavailable for tiles in corresponding pictures, quantization parameters,offsets, picture specific coding tool parameters (e.g., filtercontrols), etc. The tile group header 514 contains parameters that arespecific to each tile group in a picture. Hence, there may be one tilegroup header 514 per tile group in the video sequence. The tile groupheader 514 may contain tile group information, picture order counts(POCs), reference picture lists, prediction weights, tile entry points,deblocking parameters, etc. It should be noted that some systems referto the tile group header 514 as a slice header, and use such informationto support slices instead of tile groups.

The image data 520 contains video data encoded according tointer-prediction and/or intra-prediction as well as correspondingtransformed and quantized residual data. Such image data 520 is sortedaccording to the partitioning used to partition the image prior toencoding. For example, the image in the image data 520 is divided intoone or more tile groups 521. Each tile group 521 contains one or moretiles 523. The tiles 523 are further divided into coding tree units(CTUs). The CTUs are further divided into coding blocks based on codingtrees. The coding blocks can then be encoded/decoded according toprediction mechanisms. An image/picture can contain one or more tilegroups 521 and one or more tiles 523.

A tile group 521 is a set of related tiles 523 that can be separatelyextracted and coded, for example to support display of a region ofinterest and/or to support parallel processing. A picture may containone or more tile groups 521. Each tile group 521 references coding toolsin a corresponding tile group header 514. Accordingly, a current tilegroup 521 can be coded using different coding tools from other tilegroups 521 by altering data in a corresponding tile group header 514. Atile group 521 may be described in terms of the mechanism used to assignthe tiles 523 to the tile group 521. A tile group 521 that containstiles 523 assigned in raster scan order may be referred to as a rasterscan tile group. A tile group 521 that contains tiles 523 assigned tocreate a rectangle (or square) may be referred to as a rectangular tilegroup. FIGS. 6-7 include examples of raster scan tile groups andrectangular tile groups, respectively, as discussed in more detailbelow.

A tile 523 is a partitioned portion of a picture created by horizontaland vertical boundaries. Tiles 523 may be rectangular and/or square. Apicture may be petitioned into rows and columns of tiles 523. A tile 523row is a set of tiles 523 positioned in a horizontally adjacent mannerto create a continuous line from the left boundary to the right boundaryof a picture (or vice versa). A tile 523 column is a set of tiles 523positioned in a vertically adjacent manner to create a continuous linefrom the top boundary to the bottom boundary of the picture (or viceversa). Tiles 523 may or may not allow prediction based on other tiles523, depending on the example. For example, a tile group 521 may containa set of tiles 523 designated as a MCTS. Tiles 523 in a MCTS can becoded by prediction from other tiles 523 in the MCTS, but not by tiles523 outside the MCTS. Tiles 523 can be further partitioned into CTUs.Coding trees can be employed to partition CTUs into coding blocks, whichcan be coded according to intra-prediction or inter-prediction.

Each tile 523 may have a unique tile index 524 in the picture. A tileindex 524 is a procedurally selected numerical identifier that can beused to distinguish one tile 523 from another. For example, tile indices524 may increase numerically in raster scan order. Raster scan order isleft to right and top to bottom. It should be noted that, in someexamples, tiles 523 may also be assigned tile identifiers (IDs). A tileID is an assigned identifier that can be used to distinguish one tile523 from another. Computations may employ tile IDs instead of tileindices 524 in some examples. Further, tile IDs can be assigned to havethe same values as the tile indices 524 in some examples. In someexamples, tile indices 524 and/or IDs may be signaled to indicateboundaries of tile groups 521 containing the tiles 523. Further, thetile indices 524 and/or IDs may be employed to map image data 520associated with a tile 523 to a proper position for display.

As noted above, a tile group 521 may be a raster scan tile group or arectangular tile group. The present disclosure includes signalingmechanisms to allow a codec to support both tile group 521 types in amanner that supports increased coding efficiency and reduces complexity.A tile group flag 531 is a data unit that can be employed to signalwhether corresponding tile groups 521 are raster scan or rectangular.The tile group flag 531 can be signaled in the SPS 510 or the PPS 512,depending on the example. The tiles 523 assigned to a tile group 521 canbe signaled by indicating a first tile 532 and a last tile 533 in thebitstream 500. For example, the first tile 532 may contain a tile index524 or ID of a tile 523 in a first position in the tile group 521. Afirst position is a top left corner for a rectangular tile group and asmallest index/ID in raster scan tile group. Further, the last tile 533may contain a tile index 524 or ID of a tile 523 in a last position inthe tile group 521. A last position is a bottom right corner for arectangular tile group and a largest index/ID in raster scan tile group.

The tile group flag 531, the first tile 532, and the last tile 533provide sufficient information to allow a decoder to determine the tiles523 in a tile group 521. For example, a raster scan mechanism candetermine the tiles 523 in a raster scan tile group based on the firsttile 532 and the last tile 533. Further, a rectangular mechanism candetermine the tiles 523 in a rectangular tile group based on the firsttile 532 and the last tile 533. This allows the tile indices 524 forother tiles 523 in the corresponding tile group 521 to be omitted fromthe bitstream 500, which reduces bitstream 500 size and hence increasescoding efficiency. As such, the tile group flag 531 provides sufficientinformation to allow the decoder to determine which mechanism to employto determine which tiles 523 are assigned to the tile group 521.

Accordingly, an encoder can determine whether to use raster scan orrectangular tile groups for the bitstream 500 or sub-portions thereof.The encoder can then then set the tile group flag 531. Further, theencoder can assign tiles 523 to a tile group 521 and include the firsttile 532 and the last tile 533 in the bitstream 500. A hypotheticalreference decoder (HRD) at the encoder can then determine tile 523assignment to the tile group 521 based on the tile group flag 531, thefirst tile 532, and the last tile 533. The HRD is a set of encoder sidemodules that predict decoding results at a decoder as part of selectingan optimal coding approach during RDO. Further, the decoder can receivethe bitstream 500 and determine tile group 521 assignment based on thetile group flag 531, the first tile 532, and the last tile 533.Specifically, both the HRD at the encoder and the decoder may select araster scan mechanism or a rectangular mechanism based on the tile groupflag 531. The HRD and the decoder can then employ the selected mechanismto determine the assignment of the tiles 523 to the tile group 521 basedon the first tile 532 and the last tile 533.

The following is a specific example of the abovementioned mechanisms.

firstTileIdx = TileIdToIdx[ first_tile_id ] lastTileIdx = TileIdToIdx[last_tile_id ] if( rectangular_tile_group_flag ) {  deltaTileIdx =lastTileIdx − firstTileIdx  numTileRows = ( deltaTileIdx / (num_tile_columns_minus1 + 1 ) ) + 1  numTileColumns = ( deltaTileIdx % (num_tile_columns_minus1 + 1 ) ) + 1  NumTilesInTileGroup = numTileRows *numTileColumns  tileIdx = firstTileIdx  for( j = 0, tIdx = 0; j <numTileRows; j++, tileIdx += num_tile_columns_minus1 + 1 ) {   for( i =0, currTileIdx = tileIdx; i < numTileColumn; i++, currTileIdx++, tIdx++) {    TgTileIdx[ tIdx ] = currTileIdx } else {  NumTilesInTileGroup =lastTileIdx − firstTileIdx + 1  TgTileIdx[ 0 ] = firstTileIdx  for( i =1, i < NumTilesInTileGroup, i++)   TgTileIdx[ i ] = TgTileIdx[ i − 1 ] +1 }

In this example, the tile group flag 531, denoted asrectangular_tile_group_flag, can be employed to select a rectangularmechanism (e.g., the if statement) or a raster scan mechanism (e.g., theelse statement). The rectangular mechanism determines a delta valuebetween the first tile of the tile group and the last tile of the tilegroup. The number of tile group rows is determined by dividing the deltavalue by a number of tile columns in the picture plus one. The number oftile group columns is determined by the delta value modulo the number oftile columns in the picture plus one. The tile assignment can then bedetermined based on the number of tile group rows and the number of tilegroup columns (e.g., the for loops in the if statement). Meanwhile, theraster scan mechanism determines a number of tiles between a first tileof the tile group and a last tile of the tile group. As the tiles areindexed in raster scan order, the raster scan mechanism can then add thedetermined number of tiles to the tile group in raster scan order (e.g.,the for loop in the else statement).

FIG. 6 is a schematic diagram illustrating an example picture 600partitioned into raster scan tile groups 621. For example, the picture600 can be encoded in and decoded from a bitstream 500, for example by acodec system 200, an encoder 300, and/or a decoder 400. Further, thepicture 600 can be partitioned to support encoding and decodingaccording to method 100.

The picture 600 includes tiles 623 assigned to raster scan tile groups621, 624, and 625, which may be substantially similar to tiles 523 andtile group 521, respectively. The tiles 623 are assigned to the rasterscan tile groups 621, 624, and 625 in raster scan order on a tile 623 bytile 623 basis. To clearly depict the boundaries between the raster scantile groups 621, 624, and 625, each tile group is surrounded by anoutline in bold typeface. Further, tile group 621 is depicted by shadingto further distinguish between tile group boundaries. It should also benoted that a picture 600 may be partitioned into any number of rasterscan tile groups 621, 624, and 625. For clarity of discussion, thefollowing description relates to raster scan tile group 621. However,tiles 623 are assigned to raster scan tile groups 624 and 625 in amanner similar to raster scan tile group 621.

As shown, a first tile 623 a, a last tile 623 b, and all shaded tilesbetween the first tile 623 a and the last tile 623 b are assigned to thetile group 621 in raster scan order. As shown, a mechanism (e.g., amethod operating on a processor) proceeding according to raster scanorder assigns the first tile 623 a to the tile group 621 and thenproceeds to assign each tile 623 to the tile group 621 (from left toright) until the right picture 600 boundary is reached (unless a lasttile 623 b is reached). Raster scan order then proceeds to the next rowof tiles 623 (e.g., from top row(s) toward the bottom row(s)). In thepresent case, the first tile 623 a is on the first row, and hence thenext row is the second row. Specifically, the raster scan order proceedsto the first tile on the second row at the left picture 600 boundary,and then proceeds from left to right across the second row until theright picture 600 boundary is reached. The raster scan then moves thenext row, which is the third row in this case, and proceeds withassignment from the first tile on the third row at the left picture 600boundary. The raster scan then moves right across the third row. Thisorder continues until the last tile 623 b is reached. At this point, thetile group 621 is complete. Additional tiles 623 below and/or to theright of tile group 621 can be assigned to tile group 625 in raster scanorder in a similar manner. Tiles 623 above and/or to the left of tilegroup 621 are assigned to tile group 624 in a similar manner.

FIG. 7 is a schematic diagram illustrating an example picture 700partitioned into rectangular tile groups 721. For example, the picture700 can be encoded in and decoded from a bitstream 500, for example by acodec system 200, an encoder 300, and/or a decoder 400. Further, thepicture 700 can be partitioned to support encoding and decodingaccording to method 100.

The picture 700 includes tiles 723 assigned to a rectangular tile group721, which may be substantially similar to tiles 523 and tile group 521,respectively. The tiles 723 assigned to the rectangular tile group 721are depicted in FIG. 7 as surrounded by an outline in bold typeface.Further, selected rectangular tile groups 721 are shaded to clearlydelineate between rectangular tile groups 721. As shown, a rectangulartile group 721 includes a set of tiles 723 that make a rectangularshape. It should be noted that rectangular tile groups 721 may also besquare as a square is a particular case of a rectangle. As shown, arectangle has four sides where each side is connected to two other sidesby a right angle (e.g., a ninety degree angle). A rectangular tile group721 a contains a first tile 723 a and a last tile 723 b. The first tile723 a is at the top left corner of the rectangular tile group 721 a andthe last tile is at the bottom right corner of the rectangular tilegroup 721 a. Tiles 723 included in or between the rows and columnscontaining the first tile 723 a and the last tile 723 b are alsoassigned to the rectangular tile group 721 a on a tile by tile basis. Asshown, this scheme is different from raster scan. For example, tile 723c is between the first tile 723 a and a last tile 723 b in raster scanorder, but is not included in the same rectangular tile group 721 a.Rectangular tile groups 721 may be more computationally complex thanraster scan tile groups 621 due to the geometries involved. However,rectangular tile groups 721 are more flexible. For example, arectangular tile group 721 a may contain tiles 723 from different rowswithout containing every tile between the first tile 723 and the rightboundary of the picture 700 (e.g., such as tile 723 c). The rectangulartile group 721 a may also exclude selected tiles between the leftpicture boundary and the last tile 723 b. For example, tile 723 d isexcluded from the tile group 721 a.

Accordingly, rectangular tile groups 721 and raster scan tile groups 621each have different benefits, and hence may each be more optimal fordifferent use cases. For example, raster scan tile groups 621 may bemore beneficial when the entire picture 600 is to be displayed andrectangular tile groups 721 may be more beneficial when only asub-picture is to be displayed. However, as noted above differentmechanisms may be employed to determine which tiles are assigned to thetile group when only the first tile index and last tile index aresignaled in the bitstream. As such, a flag indicating which tile grouptype is employed can be used by the decoder or HRD to select theappropriate raster scan or rectangular mechanism. The tile assignment tothe tile group can then be determined by employing the first tile andlast tile in the tile group.

By employing the forgoing, video coding systems can be improved. Assuch, this disclosure describes various improvements to grouping oftiles in video coding. More specifically, this disclosure describessignaling and derivation processes to support two different tile groupconcepts, raster-scan based tile groups, and rectangular tile groups. Inone example, a flag is employed in a parameter set that is referred todirectly or indirectly by the corresponding tile group. The flagspecifies which tile group approach is used. The flag can be signaled ina parameter set such as the sequence parameter set, the pictureparameter set, or another type of parameter set that is referred todirectly or indirectly by tile groups. As a specific example, the flagmay be a rectangular_tile_group_flag. In some examples, an indicationwith two or more bits may be defined and signaled in a parameter setthat is referred to directly or indirectly by corresponding tile groups.The indication may specify which tile group approach is used. Using suchan indication, two or more tile group approaches can be supported. Thenumber of bits for signaling the indication depends on the number oftile group approaches to be supported. In some examples, the flag or theindication can be signaled in the tile group header.

Signaling information indicating the first tile and the last tile thatare included in the tile group may be sufficient to indicate which tilesare included in a raster-scan tile group or rectangular tile group.Derivation of tiles that are included in a tile group may depend on thetile group approach used (which may be indicated by the flag orindication), information of the first tile in the tile group, andinformation of the last tile in the tile group. The information foridentifying a particular tile can be any of the following: the tileindex, the tile ID (if different from the tile index), a CTU included inthe tile (e.g., the first CTU included in the tile), or a luma sampleincluded in the tile (e.g., the first luma sample included in the tile).

The following is a specific embodiment of the abovementioned mechanisms.A picture parameter set RBSP syntax may be as follows.

Descriptor pic_parameter_set_rbsp( ) {  . . .  tile_id_len_minus1 ue(v). . .  rectangular_tile_group_flag u(1)  . . . }

The tile_id_len_minus1 plus 1 specifies the number of bits used torepresent the syntax element tile_id_val[i][j], when present, in thePPS, and the syntax element first_tile_id and last_tile_id in tile groupheaders referring to the PPS. The value of tile_id_len_minus1 may be inthe range of Ceil(Log 2(NumTilesInPic) to 15, inclusive. Therectangular_tile_group_flag, when set equal to one, may specify thattile groups referring to the PPS include of one or more tiles that forma rectangular area of a picture. The rectangular_tile_group_flag, whenset equal to zero, may specify that tile groups referring to the PPSinclude of one or more tiles that are consecutive in raster scan orderof the picture.

The tile group header syntax may be as follows.

Descriptor tile_group_header( ) {  . . .  single_tile_in_tile_group_flag// Same as single_tile_in_slice_flag in IDF u(1) #86002675 first_tile_id // Same as top_left_tile_id in IDF #86002675 u(v)  if(!single_tile_in_tile_group_flag ) {   last_tile_id // Same asbottom_right_tile_id in IDF #86002675 u(v)  . . . }

The single_tile_in_tile_group_flag, when set equal to one, may specifythat there is only one tile in the tile group. Thesingle_tile_in_tile_group_flag, when set equal to zero, may specify thatthere is more than one tile in the tile group. The first_tile_id mayspecify the tile ID of the first tile of the tile group. The length offirst_tile_id may be tile_id_len_minus1+1 bits. The value offirst_tile_id may not be equal to the value of first_tile_id of anyother coded tile group of the same coded picture. When there is morethan one tile group in a picture, the decoding order of the tile groupsin the picture may be in increasing value of first_tile_id. Thelast_tile_id may specify the tile ID of the last tile of the tile group.The length of last_tile_id may be tile_id_len_minus1+1 bits. When notpresent, the value of last_tile_id may be inferred to be equal tofirst_tile_id.

The variable NumTilesInTileGroup, which specifies the number of tiles inthe tile group, and TgTileIdx[i], which specifies the tile index of thei-th tile in the tile group, may be derived as follows:

firstTileIdx = TileIdToIdx[ first_tile_id ] lastTileIdx = TileIdToIdx[last_tile_id ] if( rectangular_tile_group_flag ) {  deltaTileIdx =lastTileIdx − firstTileIdx  numTileRows = ( deltaTileIdx / (num_tile_columns_minus1 + 1 ) ) + 1  numTileColumns = ( deltaTileIdx % (num_tile_columns_minus1 + 1 ) ) + 1  NumTilesInTileGroup = numTileRows *numTileColumns  tileIdx = firstTileIdx  for( j = 0, tIdx = 0; j <numTileRows; j++, tileIdx += num_tile_columns_ minus1 + 1 ) {   for( i =0, currTileIdx = tileIdx; i < numTileColumn; i++, currTileIdx++, tIdx++) {    TgTileIdx[ tIdx ] = currTileIdx } else {  NumTilesInTileGroup =lastTileIdx − firstTileIdx + 1  TgTileIdx[ 0 ] = firstTileIdx  for( i =1, i < NumTilesInTileGroup, i++)   TgTileIdx[ i ] = TgTileIdx[ i − 1 ] +1 }

The general tile group data syntax may be as follows.

Descriptor tile_group_data( ) {  for( i = 0; i < NumTilesInTileGroup;i++ ) {   ctbAddrInTs = FirstCtbAddrTs[ TgTileIdx[ i ] ]   for( j = 0; j< NumCtusInTile[ TgTileIdx[ i ] ]; j++, ctbAddrInTs++ ) {    CtbAddrInRs= CtbAddrTsToRs[ ctbAddrInTs ]    coding_tree_unit( )   }  end_of_tile_one_bit /* equal to 1 */ ae(v)   if( i <NumTilesInTileGroup − 1 )    byte_alignment( )  } }

FIG. 8 is a schematic diagram of an example video coding device 800. Thevideo coding device 800 is suitable for implementing the disclosedexamples/embodiments as described herein. The video coding device 800comprises downstream ports 820, upstream ports 850, and/or transceiverunits (Tx/Rx) 810, including transmitters and/or receivers forcommunicating data upstream and/or downstream over a network. The videocoding device 800 also includes a processor 830 including a logic unitand/or central processing unit (CPU) to process the data and a memory832 for storing the data. The video coding device 800 may also compriseelectrical, optical-to-electrical (OE) components, electrical-to-optical(EO) components, and/or wireless communication components coupled to theupstream ports 850 and/or downstream ports 820 for communication of datavia electrical, optical, or wireless communication networks. The videocoding device 800 may also include input and/or output (I/O) devices 860for communicating data to and from a user. The I/O devices 860 mayinclude output devices such as a display for displaying video data,speakers for outputting audio data, etc. The I/O devices 860 may alsoinclude input devices, such as a keyboard, mouse, trackball, etc.,and/or corresponding interfaces for interacting with such outputdevices.

The processor 830 is implemented by hardware and software. The processor830 may be implemented as one or more CPU chips, cores (e.g., as amulti-core processor), field-programmable gate arrays (FPGAs),application specific integrated circuits (ASICs), and digital signalprocessors (DSPs). The processor 830 is in communication with thedownstream ports 820, Tx/Rx 810, upstream ports 850, and memory 832. Theprocessor 830 comprises a coding module 814. The coding module 814implements the disclosed embodiments described herein, such as methods100, 900, and 1000, which may employ a bitstream 500, a picture 600,and/or a picture 700. The coding module 814 may also implement any othermethod/mechanism described herein. Further, the coding module 814 mayimplement a codec system 200, an encoder 300, and/or a decoder 400. Forexample, the coding module 814 can partition an image into tile groupsand/or tiles, tiles into CTUs, CTUs into blocks, and encode the blockswhen acting as an encoder. Further, the coding module 814 can selectraster scan or rectangular tile groups and signal such selection in abitstream. The coding module 814 may also signal the first tile and lasttile to support determination of tile assignment to tile groups. Whenacting as a decoder or HRD, the coding module 814 can determine the typeof tile group used and determine the tiles assigned to the tile groupbased on the first tile and last tile. Hence, coding module 814 causesthe video coding device 800 to provide additional functionality and/orcoding efficiency when partitioning and coding video data. As such, thecoding module 814 improves the functionality of the video coding device800 as well as addresses problems that are specific to the video codingarts. Further, the coding module 814 effects a transformation of thevideo coding device 800 to a different state. Alternatively, the codingmodule 814 can be implemented as instructions stored in the memory 832and executed by the processor 830 (e.g., as a computer program productstored on a non-transitory medium).

The memory 832 comprises one or more memory types such as disks, tapedrives, solid-state drives, read only memory (ROM), random access memory(RAM), flash memory, ternary content-addressable memory (TCAM), staticrandom-access memory (SRAM), etc. The memory 832 may be used as anover-flow data storage device, to store programs when such programs areselected for execution, and to store instructions and data that are readduring program execution.

FIG. 9 is a flowchart of an example method 900 of encoding a picture,such as picture 600 and/or 700, into a bitstream, such as bitstream 500.Method 900 may be employed by an encoder, such as a codec system 200, anencoder 300, and/or a video coding device 800 when performing method100.

Method 900 may begin when an encoder receives a video sequence includinga plurality of pictures and determines to encode that video sequenceinto a bitstream, for example based on user input. The video sequence ispartitioned into pictures/images/frames for further partitioning priorto encoding. At step 901, a picture is partitioned into a plurality oftiles. Further, the tiles are assigned into a plurality of tile groups,and hence a subset of the tiles are assigned a tile group. In someexamples, the tile group is a raster scan tile group. In other examples,the tile group is a rectangular tile group.

At step 903, a flag is encoded into the bitstream. The flag can be setto a first value when the tile group is a raster scan tile group and asecond value when the tile group is a rectangular tile group. The flagmay be encoded into a parameter set of the bitstream. For example, theparameter set into which the flag is encoded may be a sequence parameterset or a picture parameter set. In some examples, the flag is arectangular tile group flag.

At step 905, an identifier of a first tile of the tile group and anidentifier of a last tile of the tile group is encoded in the bitstream.The first tile of the tile group and the last tile of the tile group maybe used to indicate the tiles assigned to the tile group. In someexamples, the identifier of the first tile of the tile group and theidentifier of the last tile of the tile group are encoded in a tilegroup header in the bitstream.

The flag, the first tile of the tile group, and the last tile of thetile group can be used by the decoder and/or by an HRD at the encoder todetermine tile assignment for the tile group. When the tile group is theraster scan tile group, as indicated by the flag, the tile assignmentfor the tile group can be determined as follows. A number of tilesbetween the first tile of the tile group and the last tile of the tilegroup can be determined as a number of tiles in the tile group. The tileassignment can then be determined based on the number of tiles in thetile group. When the tile group is the rectangular tile group, asindicated by the flag, the tile assignment for the tile group can bedetermined as follows. A delta value between the first tile of the tilegroup and the last tile of the tile group can be determined. A number oftile group rows can be determined based on the delta value and a numberof tile columns in the picture. A number of tile group columns can alsobe determined based on the delta value and the number of tile columns inthe picture. The tile assignment can then be determined based on thenumber of tile group rows and the number of tile group columns.

At step 907, the tiles are encoded into a bitstream based on tileassignment. The bitstream may also be stored for communication toward adecoder at step 909.

FIG. 10 is a flowchart of an example method 1000 of decoding a picture,such as picture 600 and/or 700, from a bitstream, such as bitstream 500.Method 1000 may be employed by a decoder, such as a codec system 200, adecoder 400, and/or a video coding device 800 when performing method100. For example, method 1000 may be employed in response to method 900.

Method 1000 may begin when a decoder begins receiving a bitstream ofcoded data representing a video sequence, for example as a result ofmethod 900. At step 1001, a bitstream is received at a decoder. Thebitstream includes a picture partitioned into a plurality of tiles. Thetiles are assigned into a plurality of tile groups, and hence a subsetof the tiles are assigned to a tile group. In some examples, the tilegroup is a raster scan tile group. In other examples, the tile group isa rectangular tile group.

At step 1003, a flag is obtained from a parameter set of the bitstream.The tile group is determined to be a raster scan tile group when theflag is set to a first value. The tile group is determined to be arectangular tile group when the flag is set to a second value. Forexample, the parameter including the flag may be a sequence parameterset or a picture parameter set. In some examples, the flag is arectangular tile group flag.

At step 1005, an identifier of a first tile of the tile group and anidentifier of a last tile of the tile group are obtained to supportdetermination of the tiles assigned to the tile group. In some examples,the identifier of the first tile of the tile group and the identifier ofthe last tile of the tile group are obtained from a tile group header inthe bitstream.

At step 1007, the tile assignment for the tile group is determined basedon whether the tile group is the raster scan tile group or rectangulartile group. For example, the flag, the first tile of the tile group, andthe last tile of the tile group can be used to determine tile assignmentfor the tile group. When the tile group is the raster scan tile group,as indicated by the flag, the tile assignment for the tile group can bedetermined as follows. A number of tiles between the first tile of thetile group and the last tile of the tile group can be determined as anumber of tiles in the tile group. The tile assignment can then bedetermined based on the number of tiles in the tile group. When the tilegroup is the rectangular tile group, as indicated by the flag, the tileassignment for the tile group can be determined as follows. A deltavalue between the first tile of the tile group and the last tile of thetile group can be determined. A number of tile group rows can bedetermined based on the delta value and a number of tile columns in thepicture. A number of tile group columns can also be determined based onthe delta value and the number of tile columns in the picture. The tileassignment can then be determined based on the number of tile group rowsand the number of tile group columns.

At step 1009, the tiles are decoded to generate decoded tiles based ontile assignment for the tile group. A reconstructed video sequence canalso be generated for display based on the decoded tiles.

FIG. 11 is a schematic diagram of an example system 1100 for coding avideo sequence of pictures, such as picture 600 and/or 700, in abitstream, such as bitstream 500. System 1100 may be implemented by anencoder and a decoder such as a codec system 200, an encoder 300, adecoder 400, and/or a video coding device 800. Further, system 1100 maybe employed when implementing method 100, 900, and/or 1000.

The system 1100 includes a video encoder 1102. The video encoder 1102comprises a partitioning module 1101 for partitioning a picture into aplurality of tiles. The video encoder 1102 further comprises anincluding module 1103 for including a number of the tiles into a tilegroup. The video encoder 1102 further comprises an encoding module 1105for encoding a flag set to a first value when the tile group is a rasterscan tile group and a second value when the tile group is a rectangulartile group, wherein the flag is encoded into a parameter set of thebitstream, and encoding the tiles into a bitstream based on the tilegroup. The video encoder 1102 further comprises a storing module 1107for storing the bitstream for communication toward a decoder. The videoencoder 1102 further comprises a transmitting module 1109 fortransmitting the bitstream to support determining the type of tilegroup(s) used and the tiles included in the tile group(s). The videoencoder 1102 may be further configured to perform any of the steps ofmethod 900.

The system 1100 also includes a video decoder 1110. The video decoder1110 comprises a receiving module 1111 for receiving a bitstreamincluding a picture partitioned into a plurality of tiles, wherein anumber of the tiles are included in a tile group. The video decoder 1110further comprises an obtaining module 1113 for obtaining a flag from aparameter set of the bitstream. The video decoder 1110 further comprisesa determining module 1115 for determining the tile group is a rasterscan tile group when the flag is set to a first value, determining thetile group is a rectangular tile group when the flag is set to a secondvalue, and determining tile inclusion for the tile group based onwhether the tile group is the raster scan tile group or rectangular tilegroup. The video decoder 1110 further comprises a decoding module 1117for decoding the tiles to generate decoded tiles based on the tilegroup. The video decoder 1110 further comprises a generating module 1119for generating a reconstructed video sequence for display based on thedecoded tiles. The video decoder 1110 may be further configured toperform any of the steps of method 1000.

A first component is directly coupled to a second component when thereare no intervening components, except for a line, a trace, or anothermedium between the first component and the second component. The firstcomponent is indirectly coupled to the second component when there areintervening components other than a line, a trace, or another mediumbetween the first component and the second component. The term “coupled”and its variants include both directly coupled and indirectly coupled.The use of the term “about” means a range including ±10% of thesubsequent number unless otherwise stated.

It should also be understood that the steps of the exemplary methods setforth herein are not necessarily required to be performed in the orderdescribed, and the order of the steps of such methods should beunderstood to be merely exemplary. Likewise, additional steps may beincluded in such methods, and certain steps may be omitted or combined,in methods consistent with various embodiments of the presentdisclosure.

While several embodiments have been provided in the present disclosure,it may be understood that the disclosed systems and methods might beembodied in many other specific forms without departing from the spiritor scope of the present disclosure. The present examples are to beconsidered as illustrative and not restrictive, and the intention is notto be limited to the details given herein. For example, the variouselements or components may be combined or integrated in another systemor certain features may be omitted, or not implemented.

In addition, techniques, systems, subsystems, and methods described andillustrated in the various embodiments as discrete or separate may becombined or integrated with other systems, components, techniques, ormethods without departing from the scope of the present disclosure.Other examples of changes, substitutions, and alterations areascertainable by one skilled in the art and may be made withoutdeparting from the spirit and scope disclosed herein.

What is claimed is:
 1. A method implemented by an encoder, the method comprising: partitioning a picture into a plurality of tiles; including a number of the tiles into a tile group; encoding a flag set to a first value when the tile group is a raster scan tile group and a second value when the tile group is a rectangular tile group, wherein the flag is encoded into a parameter set of a bitstream; encoding in the bitstream an identifier of a first tile of the tile group to indicate the tiles included in the tile group; encoding in the bitstream an identifier of a last tile of the tile group to indicate the tiles included in the tile group; encoding the tiles into the bitstream based on the tile group; and storing the bitstream for communication toward a decoder.
 2. The method of claim 1, wherein the flag is a rectangular tile group flag.
 3. The method of claim 1, wherein the parameter set into which the flag is encoded is a sequence parameter set.
 4. The method of claim 1, wherein the parameter set into which the flag is encoded is a picture parameter set.
 5. The method of claim 1, wherein the identifier of the first tile of the tile group and the identifier of the last tile of the tile group are encoded in a tile group header in the bitstream.
 6. The method of claim 1, wherein when the tile group is the raster scan tile group, tile inclusion in the tile group is determined by: determining a number of tiles between the first tile of the tile group and the last tile of the tile group as the number of tiles in the tile group; and determining the tile inclusion based on the number of tiles in the tile group.
 7. The method of claim 1, wherein when the tile group is the rectangular tile group, tile inclusion in the tile group is determined by: determining a delta value between the first tile of the tile group and the last tile of the tile group; determining a number of tile group rows based on the delta value and a number of tile columns in the picture; determining a number of tile group columns based on the delta value and the number of tile columns in the picture; and determining the tile inclusion based on the number of tile group rows and the number of tile group columns.
 8. A method implemented by a decoder, the method comprising: receiving a bitstream including a picture partitioned into a plurality of tiles, wherein a number of the tiles are included into a tile group; obtaining a flag from a parameter set of the bitstream; determining the tile group is a raster scan tile group when the flag is set to a first value; determining the tile group is a rectangular tile group when the flag is set to a second value; determining tile inclusion for the tile group based on whether the tile group is the raster scan tile group or rectangular tile group; obtaining an identifier of a first tile of the tile group to determine the tiles included in the tile group; obtaining an identifier of a last tile of the tile group to determine the tiles included in the tile group; decoding the tiles to generate decoded tiles based on the tile group; and generating a reconstructed video sequence for display based on the decoded tiles.
 9. The method of claim 8, wherein the flag is a rectangular tile group flag.
 10. The method of claim 8, wherein the parameter set including the flag is a sequence parameter set.
 11. The method of claim 8, wherein the parameter set including the flag is a picture parameter set.
 12. The method of claim 8, wherein the identifier of the first tile of the tile group and the identifier of the last tile of the tile group are obtained from a tile group header in the bitstream.
 13. The method of claim 8, wherein when the tile group is the raster scan tile group, the tile inclusion in the tile group is determined by: determining a number of tiles between the first tile of the tile group and the last tile of the tile group as the number of tiles in the tile group; and determining the tile inclusion based on the number of tiles in the tile group.
 14. The method of claim 8, wherein when the tile group is the rectangular tile group, the tile inclusion in the tile group is determined by: determining a delta value between the first tile of the tile group and the last tile of the tile group; determining a number of tile group rows based on the delta value and a number of tile columns in the picture; determining a number of tile group columns based on the delta value and the number of tile columns in the picture; and determining the tile inclusion based on the number of tile group rows and the number of tile group columns.
 15. A method implemented by a decoder, the method comprising: receiving a bitstream comprising a group of tiles in a picture and a parameter set containing a flag, wherein when the flag is set to a first value, the flag specifies a raster scan mode is in use for the group of tiles in the picture, and wherein when the flag is set to a second value, the flag specifies a rectangular mode is in use for the group of tiles in the picture, wherein a raster scan group of tiles contains tiles in consecutive raster scan order of the picture, and a rectangular group of tiles contains tiles collectively forming a rectangular region of the picture; and decoding the group of tiles based on the flag.
 16. The method of claim 15, wherein the parameter set containing the flag is a picture parameter set.
 17. The method of claim 15, wherein an identifier of a first tile of the group of tiles indicates tiles included in the group of tiles.
 18. A method implemented by a decoder, the method comprising: receiving a bitstream comprising a group of tiles in a picture and a parameter set containing a flag, wherein when the flag is set to a first value, the flag specifies a raster scan mode is in use for the group of tiles in the picture, and wherein when the flag is set to a second value, the flag specifies a rectangular mode is in use for the group of tiles in the picture; determining delta values specifying indices of a first tile of each group of tiles; and decoding the group of tiles based on the flag and the delta values. 